The invention is used in technical fields in which power semiconductors are used to control high voltages, typically at least several thousand volts, or high currents, typically at least several hundred amperes. This is the case, for example, in the field of power supply.
Switches for high voltages are usually in the form of mechanical switches in which two contacts are isolated from one another by moving at least one contact with generation of a spark or an arc. This requires the design and construction of a switch drive and also energy stores, catches and controllers for the drive and arc-resistant switching contacts.
The structural outlay for switches of this type may, in principle, be considerably reduced by using semiconductor elements.
However, it is difficult to use power semiconductors in high power ranges on account of the limited dielectric strength and current-carrying strength.
For this reason, switches for switching high voltages are formed from components which are electrically connected in series. Switches of this type are used, for example, for high-voltage DC transmission where AC voltages of several hundred kilovolts (kV) are rectified using semiconductors and are converted to AC voltage again at the end of a long transmission path. On the one hand, this minimizes the resistive power loss by virtue of the use of a high voltage and, on the other hand, keeps the dielectric loss (as a result of capacitive and inductive loads) low by virtue of rectification.
Since a relatively large number of semiconductor components are used in series circuits of this type, the failure of individual components during operation must be expected. It is therefore customary, in a series circuit of this type, to arrange more components than would be required to achieve the requisite dielectric strength. The individual components are embodied in such a manner that, in the case of a functional disturbance, they reliably change into a permanently conducting state and the redundancy is such that, in total, the remaining functioning semiconductors have the requisite dielectric strength.
This function of a component changing into a reliably conducting state in the case of failure or a functional disturbance has hitherto been achieved by using pressure-contact designs in the form of disk-type thyristors (presspack, hockey puck). This is known, for example, for thyristors and diodes. In the event of a breakdown of the silicon chip, this achieves a short circuit between the solid electrode plates which are pressed onto both sides of the silicon chip. The short circuit is produced by fusing of the respective silicon chip.
The design in presspack housings is also known for IGBTs (IGBT=Insulated Gate Bipolar Transistor). However, the MOS structures (MOS=Metal Oxide Semiconductor) on the top side of the chip of IGBTs give rise to technological disadvantages. The fabrication methods for IGBTs in presspack housings are therefore very complicated and expensive.
In order to control currents of high current intensity, it is also conceivable to provide a parallel circuit of semiconductor modules which each carry partial currents. In this case, when a semiconductor module becomes conductive as a result of a functional disturbance, this results in the entire parallel circuit and thus the semiconductor circuit arrangement becoming conductive for the current. In this case, it is thus not possible to operate with a component in the form of a presspack but rather, in the event of a functional disturbance, it must be ensured that the semiconductor module is isolated from the circuit arrangement or at least from the current path.
Against the background described, the object on which the present invention is based is to ensure that, in the case of a semiconductor circuit arrangement for controlling a high voltage and in the case of a semiconductor circuit arrangement for controlling a current of high current intensity of the type mentioned initially, the circuit arrangement is guaranteed to function even in the case of a functional disturbance in, or the failure of, individual semiconductor modules.